Four-wheel and all-wheel drive vehicles are popular for their enhanced capabilities in inclement weather and off-highway conditions as compared with two-wheel drive vehicles. In order to further boost these capabilities, modern four-wheel and all-wheel drive vehicles frequently employ a limited slip differential (LSD) between two respective rear axle-shafts in place of a more common open type differential. Some high performance four-wheel and all-wheel drive vehicles employ a limited slip differential in the front axle, as well, while others go a step further in utilizing a centrally located limited slip differential, i.e. between the axles.
By limiting the velocity difference between a pair of wheels driven by their respective axle half-shafts, an LSD can transmit useful torque as long as there is some friction available at the interface between the ground and at least one of the driven wheels. Limited slip differentials couple, i.e. operationally lock, the respective axle half-shafts when the difference in the axle-shafts' rotational velocity rises above a certain preset value. Two main types of limited slip differentials are used on motor vehicles. One type is torque sensitive, which is usually either geared or clutch-pack based, and the other type is speed sensitive, which is mainly viscous or pump and clutch-pack based. Speed sensitive limited slip differentials generally have been more popular than the torque sensitive types because they are mechanically less complex and tend to require less maintenance.
Pump and clutch-pack speed sensitive LSDs generally utilize a pump, typically a gerotor, for hydraulically compressing the clutch pack. When driving conditions produce a difference in wheel rotation, the pump pressurizes its working fluid into the clutch pack area, which provides a clamp load for frictional resistance to couple the two respective axle half-shafts and thereby transfer torque to the wheel with higher traction.
However, additional pump and clutch-pack related components collectively result in a relatively large LSD assembly which can cause packaging issues as attempts are made to package current four-wheel and all-wheel drive technology into smaller vehicles. The additional components also tend to increase parasitic drag inside the LSD assembly, which may have a considerable negative impact on the vehicle's fuel efficiency.
In view of the above, an improved hydraulically locking limited slip differential with hydraulic locking capability and fewer internal components would be most beneficial in designing smaller vehicles.